1. Field of the Invention
The present invention relates to a method for etching a platinum thin film, and more particularly, to a method for dry-etching a platinum thin film whereby a clean platinum thin film can be formed by restraining redeposition of platinum.
2. Description of Related Art
Platinum thin films usually are used for forming an electrode of a thin film form for a ferroelectric capacitor as a device constituting a non-volatile random access memory or a dynamic random access memory. Here, a process for etching the platinum thin film is required to pattern the platinum thin film to form an electrode of the ferroelectric capacitor. In this etching processes, a dry etching method and a wet etching method are mainly used. The wet etching method is inconvenient because it is usually performed at a high temperature of over 60.degree. C., and, in particular, is inadequate for forming a finely-patterned platinum thin film for an electrode necessary for a highly-integrated memory for high record density. Therefore, the dry etching method is generally used to etch the platinum thin film for electrode.
Because it is difficult to etch platinum due to its characteristics of low reactivity with a general gas, it is known to use the dry etching method whereby the platinum thin film is etched using a species such as a radical, an ion, or an electron which are reactive within plasma produced by using an inert gas such as Ar, He, etc. and a reactive gas. In such a dry etching method, Ar gas or a mixed gas such as Cl.sub.2 /Ar, C.sub.2 F.sub.6 /Ar or Cl.sub.2 /C.sub.2 F.sub.6 /Ar is widely used. As for the Ar gas and the C.sub.2 F.sub.6 /Ar mixed gas, they do not make a reaction by-product through reaction with platinum, and the platinum therefore usually is etched through sputtering using Ar. Accordingly, the sputtered platinum is redeposited on the side surface of a photoresist starting from the side surface of the platinum thin film being etched, as shown in FIG. 1.
Referring now to FIG. 1, reference numeral 1 is a substrate, reference numeral 2 is a platinum pattern which is formed by an etching process, reference numeral 3 is a photoresist which is used during the etching process in order to form the platinum pattern 2, and reference numeral 4 is a platinum thin film redeposited during the etching. The reason why the unnecessary platinum thin film 4 is formed is because some by-product materials produced by the reaction of the Cl.sub.2 /Ar and Cl.sub.2 /C.sub.2 F.sub.6 /Ar mixed gases with platinum are not completely vaporized due to their high evaporation temperature. Consequently, a portion thereof is redeposited on the side surface of the platinum thin film starting from the surface of the photoresist.
As described above, the platinum thin film 4 of the prior art that is redeposited during formation of the electrode for the ferroelectric capacitor is connected to upper electrodes thus short-circuiting the capacitor. Also, other various problems may occur during deposition of an insulating layer after the platinum etching process or during the etching process for realizing a fine pattern. Thus, there exists a need to provide a dry etching process that does not result in or restrains or prevents redeposition of a platinum thin film during the etching process.